FABRIC-3.10.8 MC-3b: waking a worker core

Each worker core sets up its own IPI receiver before going online (amd64
LAPIC + vector 0x22 with its own stub, aarch64 banked GIC SGI 0, riscv64
sie.SSIE); core 0 sends by ICR / GICD_SGIR / SBI IPI. Park lets exactly
one interrupt in without a lost-wake window. Boot self-test: IPI round
trips 3/3 and 'woke x3, IPIs x3' on all three ISAs; worker vCPU threads
0.0% on the host. 3-ISA acceptance clean.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

include/starkernel/smp.h

@@ -64,4 +64,16 @@ void arch_smp_park_once(void);
  * exception level, the privilege mode), as a short phrase for its line. */
 const char *arch_smp_arrival(const sk_percpu_t *pc);
 
+/* MC-3b. On the secondary core, before it reports online: set up its own
+ * interrupt receiver for the IPI only, and record in pc->ipi_target how
+ * to reach it. */
+void arch_smp_secondary_init(sk_percpu_t *pc);
+
+/* MC-3b. Send the wake IPI to the core `target` describes. */
+void arch_smp_send_ipi(const sk_percpu_t *target);
+
+/* MC-3b. Called by each ISA's interrupt handler when the IPI arrives: counts
+ * it in this core's block. The handler acknowledges it. */
+void sk_smp_ipi_received(void);
+
 #endif /* STARKERNEL_SMP_H */